1. Technical Field
The disclosure relates to a method of preparing 3,4-ethylenedioxythiophene. More particularly, the disclosure relates to a method of preparing 3,4-ethylenedioxythiophene by microwaving instead of conventional heating.
2. Description of Related Art
3,4-ethylenedioxythiophene (EDOT) is conventionally used as a monomer to prepare Poly(3,4-ethylenedioxythiophene) (PEDOT). Since PEDOT has the properties of high conductivity, high transparency, good heat resistance, good hydrolysis resistance, and easy processing, PEDOT is widely used in photoelectric applications, such as organic light emitting diodes (OLEDs), solar cells, organic thin film transistors (OTFT), super capacitors, and electron transporting layers of flexible electronic papers etc.,
Many synthesis methods of EDOT have been studied and discussed by many scholars. However, the EDOT synthesis methods still have problems of low yield, long reaction time or environmental damage etc.
Early in 2000, Groenendaal and Jonas et al. had disclosed a method of heating 2,2′-thiodiacetic acid to perform the esterification, condensation, etherification, hydrolysis, and decarboxylation reactions of EDOT synthesis process. Although the supply source of the starting material was quite stable and the reaction condition wais mild, the problems of long reaction time and low yield made this method cannot efficiently produce EDOT (Adv. Mater. 2000, 12, 481).
In 2004, Fredrik et al. disclosed a method having easier steps to synthesize EDOT. However, the starting material, 2,3-dimethoxy-1,3-butadiene, could not be easily obtained and was high price.
Hence, the greatly increased cost did not facilitate mass production by the industry (Tetrahedron Letters 2004, 45, 6049).
Furthermore, many other scholars studied various starting materials, solvents, or catalysts to improve the yield of a certain step in the EDOT is synthesis and thus the EDOT yield. For example, in 2001, Halfpenny used disodium salt of 2,5-diethoxycarbonyl-3,4-dihydroxythiophene as the starting material to react with haloalkane and then hydrolyze the product. Finally, quinoline and Cu2O were respectively used as solvent and catalyst for the decarboxylation reaction to obtain EDOT. However, the amount of the solvent residue was too high, the solvent was toxic, and the yield was only limitedly improved. Therefore, this method was not suitable for mass production (J. Chem. Soc. Perkin Trans. 1 2001, 2595).
Accordingly, a method of preparing 3,4-ethylenedioxythiophene (EDOT) with high yield and fast reaction rate is still needed.